1. Field of the Invention
The present invention is related to a current circuit and method thereof and more particularly related to a current control circuit and method thereof for a power converter, which implements a current sampling circuit to sample an inductor current passing through the current control circuit of the power converter so as to be able to control the output duty cycle ratio. As a result, the occurrence of inrush current is restrained. The present invention provides a better response speed and better system stability.
2. Description of the Prior Art
Because of continuing development of the modern technology and the popularity of the electronic devices, power converters play an important role to the electronic devices. A power converter is to convert power to suitable voltage as needed by the electronic devices, such as computers, display monitors, DVD players, and so on.
FIG. 1 is a view illustrating a conventional power converter. The control circuit 100 includes a converter unit 101, a voltage divider circuit 102, a differential amplifier 103, a comparator 104, a compensation circuit 105 and a driver 106. An input power Vi is converted by the converter unit 101 to generate a output power V0 to a capacitance C. The converter unit 101 includes an inductor, a diode and a transistor switch. During operation, as the transistor switch is conducted, the diode will have a reverse bias to store the power of the input voltage Vi in the inductor. When the transistor switch is cut off, the inductor will be unable to store power and the power stored in the inductor will be released to the capacitance C.
The output voltage V0 will generate a feedback voltage VFB by passing the voltage of the resistor R1 and resistor R2, which are connected in serial, in the voltage divider circuit 102 to compare in the differential amplifier 103 with a reference voltage Vref to generate an error signal E0 to the comparator 104. However, it is easy to cause circuit unstable because of the effect of the loading variation. Therefore, a compensation circuit 105 is used to solve the problem of the circuit stability. At the same time, the inductor current within the converter unit 101 and a ramp signal will be weighted to generate an output signal Vsum. Thereafter, the comparator 104 will compare the error signal E0 and the output signal to generate a driving signal S′ and then the driver 106 will drive the transistor switch SW to operate.
However, the conventional power converter is likely to generate an inrush current which causes the circuit to malfunction and decreases the circuit efficiency. Therefore, it is necessary to design a power converter to solve the problem caused by the inrush current and to increase system efficiency.
The present invention is related to a current circuit and method, more particularly related to a current control circuit and method for a power converter. The invention implements a current sampling circuit to sample an inductor current passing through the current control circuit of the power converter so as to be able to control the output duty cycle ratio. As a result the occurrence of inrush current is restrained. The present invention thus provides a better response speed and better system stability.